Thread: Build and Intro
Solder off the mosfets one by one and check them with multimeter like this
Testing a MosFet
but first solder off the large resistors and check their resistance, you can check them with basic diode (continuity) test and as they are low ohms will seem like a short, they are broken if there is no reading at all.
I fried 2 drives and nothing but a mosfet and the resistor got fried inside :)
and you have to solder them off the board because the readings won't be correct while its connected to other components.
Last edited by danilom; 11-11-2013 at 08:20 PM.
Thanks for your help. Its appreciated.
The day before last a spent the day going through the driver, taking mosfets out and checking them. Well using the test you posted one of them gave different results compared to the other 4 I tested. I left 3 in there as I assumed they would be still working , ,maybe I should have tested those too as its still not working?? Anyway I replaced the bad mosfet with a new one and went to try it straight away and the fuse blew. Am I meant to test the other two smaller mosfets on the upper side of the board with the rest of the circuitry?
I had a bit of trouble measuring the resistors. The first one is 0.05 ohms(from colours), which seems very low to me. Not even sure if you can get them that low? I then tested the other two resistors which have much higher resistance (going by colours) and they came up at about 1 ohm resistance if I remember correctly. The thing is though I measured the same resistors out of a board that was working and they gave the same readings. Starting to think maybe my electrical meter isn't working properly.
I'm also wondering why the over voltage protection didn't do its job also?
Last edited by swisscheese; 14-11-2013 at 03:35 AM.
When components are still soldered into the board the results can be miles away due to parallel components. You should test everything you can and you are in an ideal situation because comparative tests can be made against the working board. Can't you test your meter on a known resistor ?
Last edited by EddyCurrent; 14-11-2013 at 09:15 AM.
The thing that gets me is that I measure the resistors from the working board and I get the same result as measuring the resistors from the stuffed board, however the reading is nowhere near where it should be, i get about 1 ohm for a 18000 ohm resistor.
Just before I swapped a resistor over and put a new mosfet in one that I though may have been broken. Went and plugged the driver in and it worked!!! Was happy so then sat down wiring everything up to go, go and turn it on and now there's nothing, doesn't even blow fuses anymore, just nothing. Anyway I've swapped in so many different mosfets from things i have lying around, think I've given up and will just wait till the new one arrives. Thanks again for everyones help.
Eddy I've been taking the components out when measuring. And the meter seems to work fine on every other resistor but the ones from the drivers!!!
I'm having some problems with the limit switches. I'm using LinuxCNC. For each axis they are wired in series and are done so when a limit is hit the circuit is broken(normally closed?). Anyway I've tried every combination and when I start up Linux CNC and press the 'power' button on the screen it straight away comes up with limit reached. I have inversed it in the stepcon. Same thing happens. I then put a little bit of wire in one of the x limit terminals and then just looped it straight back to the second x limit terminal and this fixed the problem, however obviously having it set up like this is no use. It's almost like the long wire and 2 switched delay the return signal so it thinks a limit has been reached. Another thing, it works fine if I set it to E-stop. Anyone had anything similar to this?
I'm also having a fair bit of trouble with my pulleys on the x axis(largest axis on my build). The set screws seem to keep coming loose. I thread locked them but this didn't help. Kind of made it worse. They loosened and then when I went to undo them they were jammed, ended up having to drill them out!! :(
I think I'll have to give the alloy pulleys the boot and get some steel pulleys. I just don't think they're up to the task, especially with only 8mm D shaft and only 15mm long when the pulley is 28mm wide.
I also want to put less stress on the machine overall, I had it set at about 800mm/s^2 for accel. I think I might drop this back a bit? Also will probably drop the max velocity back a bit also. It can do 11m/min just on the x axis but have it set at about 7m/min now(pulleys came loose at this speed) but think I'll drop it down again to about 5m/min. Acceleration would be the killer though with respect to forces experienced by all the componants.
Last edited by swisscheese; 15-11-2013 at 11:48 AM.
Regarding the limit switches, have you checked with a multimeter what reading you're getting at the BOB?
I've just had a quick look at a photo of the bob, and with the switched not actuated, the voltage between the two connectors should be near 0V.
Heres a vid, notice only two axis running, third done by hand
DIY CNC router - YouTube
Last edited by swisscheese; 19-11-2013 at 01:24 AM.
Just measuring voltage at the terminals, does the voltage change when you actuate the switch?
Does the limit switch problem occur when nothing else is powered up on the machine i.e. spindle not running, stepper motors not running ?
If the answer is yes then it sounds like a bad connection or a faulty switch, if the answer is no then you may be getting induced voltage into the limits wiring.
Sorry if this seems too basic but I have seen these giving bad connections in real life situations; wires pushed too far into terminals so screw grips insulation, wire that looks like it's 'bare' but has a coating of clear lacquer, badly soldered joints that connect intermittently, wire where the insulation is intact but the metal core is broken, terminals that are tight but the wire has been inserted incorrectly (it missed the hole) and is not being clamped.
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